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Magnet Calculators Surface field, pull force, repulsion, gap field, and unit conversions for neodymium magnets.

Surface Field Calculator

On-axis magnetic flux density (B) at any distance from the pole face of an axially magnetized neodymium magnet.

Inches Millimeters
Results
Formula (disc/cylinder on-axis):
B(z) = (Br/2) × [ (L+z)/√(R²+(L+z)²) − z/√(R²+z²) ] Ring: B = B_outer(z) − B_inner(z) (superposition) Block: equivalent disc radius R = √(W×D/π)

Pull Force Calculator

Tensile force to pull a neodymium magnet away from a flat steel surface. Uses the Maxwell stress method.

Inches Millimeters
Results
Maxwell Stress Method:
F = B² × A / (2μ₀) μ₀ = 4π × 10⁻⁷ T·m/A A = pole face area (m²), B = surface flux density (T)
Real-world pull is typically 50–75% of theoretical due to surface finish, coatings, thin steel, or angled separation.

Repulsion Force Calculator

Repulsion force between two identical disc/cylinder magnets with like poles facing across a gap.

Inches Millimeters
Results
Method: Field of one magnet evaluated at the gap distance from its face, applied via Maxwell stress to the opposing pole face area.
B_gap = cylinderField(Br, R, L, gap) F_rep = B_gap² × A / (2μ₀)
Most accurate for gap ≥ 10% of magnet diameter.

Gap Field Calculator

Magnetic flux density at the center of a gap between two identical disc/cylinder magnets with opposite poles attracting.

Inches Millimeters
Results
Superposition method: Each magnet contributes its field at distance gap/2 from its face; fields add at the midpoint.
B_center = 2 × B_single(z = gap/2)
Assumes free space. Nearby ferromagnetic material will increase the gap field.

Magnetic Unit Converter

Type in any field to convert instantly across all units in that category.

Magnetic Flux Density (B)
Field Strength (H)
Force
Length
Max Energy Product (BH)max

Our calculators are intended for reference purposes only. All values are approximate and should not be used as the sole basis for engineering or product design decisions. Actual magnetic performance may vary depending on application conditions and magnet configuration. Users are encouraged to validate results through testing. MagneticsPro.com accepts no liability for the use of this tool.

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